Wireless power transfer systems enable power to be transferred wirelessly from a source to a load. Inductive power transfer is a non-radiative, or near-field, type of wireless power transfer. Inductive power transfer uses an oscillating current passing through a primary coil (i.e., a transmit antenna) of a source to generate an oscillating magnetic near-field that induces currents in a secondary coil (i.e., a receive antenna) of a load. The source includes a power converter having power transistor switches which switch at controllable times to convert power of the source into the oscillating current passing through the primary coil.
Inductive power transfer is performed to wirelessly charge a load, such a traction battery of an electric vehicle, using power from the source. In such wireless electric vehicle charging systems, the transmit antenna of the source is embedded in a “charging” mat and the receive antenna (and an associated rectifier) is embedded in a designated location of the vehicle. The inductive power transfer involves inductive coupling between the antennas. For inductive power transfer to be efficient, the spacing between the antennas must be relatively close within small offset tolerances.
Ideally, the receive antenna of the vehicle only receives power transferred from the transmit antenna in the charging mat. Practically, the receive antenna of the electric vehicle is an LC resonant circuit that can receive power from any inductive power source and transfer it to the traction battery if the signal frequency is close to LC resonant frequency of the receive antenna. Unexpected power from stray power sources can damage the traction battery. Much of the control electronics in a wireless charger on the vehicle side are only powered during normal charging by a low-voltage battery (e.g., by a 12-volt battery). Thus, the control electronics cannot disconnect the wireless charger output when a magnetic near-field signal is received from a stray power source. Moreover, during normal wireless charging, if low voltage battery is somehow disconnected from the wireless charger, and the control electronics lose power, wireless communication between the charger and the source will likewise be lost. Absent this wireless communication with the power source, effective control of the charging operation may be relinquished, potentially damaging the traction battery.